Universal opt-in replay protection?

The discussion revolves around the implementation of a blockchain policy where the committed height must be at least 100 blocks in the past. This measure ensures reorganization safety, akin to the maturity period for coinbase transactions, and effectively mitigates risks associated with free relay and short-reorganization bribes. However, there is a debate about the necessity and desirability of this policy in scenarios where its benefits are most significant. It is suggested that such restrictive measures might be relaxed when expedient without undermining the system's integrity.

Additionally, the policy does not safeguard users against certain fraudulent schemes involving partially signed Bitcoin transactions (PSBT), such as those involving presigned exit, refund, or claim clauses tied to nonexistent previous blocks. In these cases, the depth of block commitment is irrelevant as the transaction's validity is compromised from inception. Software designed with fork awareness could alert users to these issues, allowing them to make informed decisions about engaging with such commitments.

In practical applications, particularly within the context of lightning networks, wallets may choose to reject transactions based on security protocols related to the ancestral depth of a UTXO. For instance, a wallet might refuse a swap against a PSBT spending a UTXO with an ancestral commitment that is less than 100 blocks deep. This is considered a reasonable security measure to prevent potential frauds and enhance transaction integrity within the network.